From wherever you like.
.WAV files are a common file type for sound. You can find many downloadable on the internet, or make your own using your phone or computer.
The LASR Community (globe button on the main screen of LASR) also includes a user-driven library of custom sound files that you can download and use to your heart's content. You do need to unlock the "library access" rank to gain access to this within the community.